Module I Course Overview And Introduction To Operating Systems CS354 ± module 1 1 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. COURSE MOTIVATION AND SCOPE Scope This is a course about the design and structure of computer operating systems. It covers the concepts, principles, functionality, tradeoffs, and implementation of systems that support concurrent processing. CS354 ± module 1 3 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. What We Will Cover d Operating system fundamentals d Functionality an operating system offers d Major system components d Interdependencies and system structure d The key relationships between operating system abstractions and the underlying hardware (especially processes and interrupts) d A few implementation details and examples CS354 ± module 1 4 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. What You Will Learn d Fundamental ± Principles ± Design options ± Tradeoffs d How to modify and test operating system code d How to design and build an operating system CS354 ± module 1 5 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. What We Will NOT Cover d A comparison of large commercial and open source operating systems d A description of features or instructions on how to use a particular commercial system d A survey of research systems and alternative approaches that have been studied d A set of techniques for building operating systems on unusual hardware CS354 ± module 1 6 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. How Operating Systems Changed Programming d Before operating systems ± Only one application could run at any time ± The application contained code to control speci®c I/O devices ± The application had to overlap I/O and processing d With an operating system in place ± Multiple applications can run at the same time ± An application is not built for speci®c I/O devices ± A programmer does not need to overlap I/O and processing ± An application is written without regard to other applications CS354 ± module 1 7 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. Why Operating Systems Are Dif®cult To Build d The gap between hardware and high-level services is huge ± Hardware is ugly ± Operating system abstractions are beautiful ± An operating system must bridge the gap between low-level hardware and high- level abstractions d Everything is now connected by computer networks ± An operating system must offer communication facilities ± Distributed mechanisms (e.g., access to remote ®les) are more dif®cult to create than local mechanisms CS354 ± module 1 8 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. An Observation About Ef®ciency d Our job in Computer Science is to build beautiful new abstractions that programmers can use d It is easy to imagine magical new abstractions d The hard part is that we must ®nd abstractions that map onto the underlying hardware ef®ciently d We hope that hardware engineers eventually build hardware for our abstractions (or at least build hardware that makes out abstractions more ef®cient) CS354 ± module 1 9 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. The Once And Future Hot Topic d In the 1970s and early 1980s, operating systems was one of the hottest topics in CS d By the mid-1990s, OS research had stagnated d Now things have heated up again, and new operating systems are being designed for ± Smart phones ± Multicore systems ± Data centers ± Large and small embedded devices (the Internet of Things) CS354 ± module 1 10 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. XINU AND THE LAB Motivation For Studying A Real Operating System d Provides examples of the principles d Makes everything clear and concrete d Shows how abstractions map to current hardware d Gives students a chance to experiment and gain ®rst-hand experience CS354 ± module 1 12 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. Can We Study Commercial Systems? d Windows ± Millions of line of code ± Proprietary d Linux ± Millions of line of code ± Lack of consistency across modules ± Duplication of functionality with slight variants CS354 ± module 1 13 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. An Alternative: Xinu d Small Ð can be read and understood in a semester d Complete Ð includes all the major components d Elegant Ð provides an excellent example of clean design d Powerful Ð has dynamic process creation, dynamic memory management, ¯exible I/O, and basic Internet protocols d Practical Ð has been used in real products CS354 ± module 1 14 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. The Xinu Lab d Innovative facility for rapid OS development and testing d Allows each student to create, download, and run code on bare hardware d Completely automated d Handles hardware reboot when necessary d Provides communication to the Internet as well as among computers in the lab CS354 ± module 1 15 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. How The Xinu Lab Works d A student ± Logs into a conventional desktop system called a front-end ± Modi®es and compiles a version of the Xinu OS ± Requests a computer to use for testing d Lab software ± Allocates one of the back-end computers for the student to use ± Downloads the student's Xinu code into the back-end ± Connects the console from the back-end to the student's window ± Allows the student to release the back-end for others to use CS354 ± module 1 16 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. REQUIRED BACKGROUND AND PREREQUISITES Background Needed d A few concepts from earlier courses ± Integer arithmetic ± Logical operators and, or, and not ± I/O: you should know the difference between standard library functions (e.g., fopen, putc, getc, fread, fwrite) and system calls (e.g., open, close, read, write) ± File systems and hierarchical directories ± Symbolic and hard links ± File modes and protection d Concurrent programming experience: you should have written a program that uses fork or threads CS354 ± module 1 18 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. Background Needed (continued) d An understanding of runtime storage components ± Segments (text, data, and bss) and their layout ± Runtime stack used for function call; argument passing ± Basic heap storage management (malloc and free) d C programming ± At least one nontrivial program ± Comfortable with low-level constructs (e.g., bit manipulation and pointers) CS354 ± module 1 19 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. Background Needed (continued) d Working knowledge of basic Unix tools (needed for programming assignments) ± Text editor (e.g., emacs) ± Compiler / linker / loader ± Tar archives ± Make and Make®les d Desire to learn CS354 ± module 1 20 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. Course Syllabus See the handout or download from Brightspace CS354 ± module 1 21 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. How We Will Proceed d We will examine the major components of an operating system d For a given component we will ± Outline the functionality it provides ± Understand principles involved ± Study one particular design choice in depth ± Consider implementation details and the relationship to hardware ± Quickly review other possibilities and tradeoffs d Note: we will cover components in a linear order that allows us to understand one component at a time without relying on later components CS354 ± module 1 22 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. A FEW THINGS TO THINK ABOUT Real concurrency Ð in which one program actually continues to function while you call up and use another Ð is more amazing but of small use to the average person. How many programs do you have that take more than a few seconds to perform any task? (From an article about new operating systems for the IBM PC in the New York Times, 25 April 1989) d CS354 ± module 1 24 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. Perfection [in design] is achieved not when there is nothing to add, but rather when there is nothing more to take away. ± Antoine de Saint-Exupery CS354 ± module 1 25 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. Questions? Introduction To Operating Systems (Definitions And Functionality) What Is An Operating System? d Answer: a large piece of sophisticated software that provides an abstract computing environment d An OS manages resources and supplies computational services d An OS hides low-level hardware details from programmers d Note: operating system software is among the most complex ever devised CS354 ± module 1 28 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc. All rights reserved. Example Services An OS Supplies d Support for concurrent execution (multiple apps running at the same time) d Process synchronization d Process-to-process communication mechanisms d Process-to-process message passing and asynchronous events d Management of address spaces and virtual memory support d Protection among users and running applications d High-level interface for I/ O devices d File systems and ®le access facilities d Internet communication CS354 ± module 1 29 Fall, 2021 Copyright 2021 by Douglas Comer and CRC Press, Inc.